Unconventional reservoirs are commonly drilled using oil-based mud, creating drill cuttings that are contaminated with hydrocarbons. Drill cuttings disposal is regulated by the state. The drill cuttings are usually disposed of by trucking them to a landfill. The economic and environmental impact is a challenge to the industry. In this study, we have investigated the feasibility of disposing of drill cuttings at the well site by mixing them into the proppant slurry as a part of the proppant during multi-stage hydraulic fracturing. Our study focused on whether the addition of drill cuttings, often composed of very fine particles, significantly impair the conductivity of the proppant pack created in the reservoir. The study provides an environmentally friendly solution to the drill cutting disposal problem with the procedures and limitations, and it helps to reduce the cost of fracturing operations.

Using actual drill cuttings samples from an Eagle Ford well, we have measured the fracture conductivity of mixtures of proppant and drill cuttings for a wide range of drill cuttings fractions. The cuttings-sand mixtures were evaluated following a modified API RP-61 procedure. A conductivity cell was used to perform short-term conductivity experiments applying dry nitrogen gas as fluid, with closure stress applied in incremental steps of 1000 psi from 1000 to 6000 psi. The cuttings were evaluated wet, as received from the rig site after mechanical separation on site, and dried, after being washed for removal of drilling fluid, to compare the effect of drilling fluid in conductivity responses. The effect of cuttings size and chemical composition on conductivity was also studied. 40/70 and 100 mesh sand were used as the proppant.

The results showed that adding up to 25% drill cuttings to the proppant pack had an insignificant effect on the fracture conductivity. The 100-mesh sand proppant retained conductivity with drill cuttings added somewhat better than the 40/70 mesh sand proppant. Because the volume of drill cuttings created in drilling even a quite long lateral is much less than the volume of proppant pumped in just a single stage, our results show that drill cuttings could be disposed of by adding them to the proppant slurry at a rate less than 25% of the proppant rate without causing any deleterious effect on the fracture conductivity created.

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